The mechanisms of premature ovarian failure are being explored by; studying families with heritable premature ovarian failure, mathematical models of functional ovarian lifespan, and rodent models of ovarian development. Families with hereditary premature ovarian failure have been studied; karyotypic abnormalities, anti-ovarian antibodies, or exposures to known ovarian toxins have not been identified in these families. Mathematical models of functional ovarian lifespan suggest that the age of menopause is only weakly affected by oocyte number. The rate of atresia appears to have a more profound effect on the duration of functional ovarian lifespan. Prenatal galactose treatment decreases the number of small follicles in both mice and rats. Primordial germ cell counts in rat embryos suggests that galactose is not toxic, but rather blocks migration.